The present invention relates, in general, to equalization of data signals, and more particularly, to adaptive equalization of data signals.
A common problem encountered when electronically transmitting data is that it becomes corrupted by such things as background noise, impulse noise, fades, etc. Usually this data corruption is a statistical phenomenon which causes additive and/or multiplicative transformations to the originally transmitted data. Thus, the original data undergoes changes such as frequency translation, nonlinear or harmonic distortion, and time dispersion. In addition, high speed data transmission over channels of limited bandwidth results in a type of distortion commonly referred to as intersymbol interference.
One technique for reducing intersymbol interference includes equalizing the data using an equalizer that compensates for the average of the range of expected channel amplitude and delay characteristics. Techniques for equalizing data are discussed in U.S. Pat. No. 5,243,624, entitled "METHOD AND APPARATUS FOR UPDATING COEFFICIENTS IN A COMPLEX ADAPTIVE EQUALIZER", which is issued to Paik et al., assigned to General Instrument Corporation, and is hereby incorporated herein by reference. As noted by Paik et al., prior art adaptive equalizers suffer from a relatively long convergence time for a least means square (LMS) algorithm. Another limitation of the prior art equalizers is that since they are implemented in digital circuitry, the data must be quantized prior to being processed by, for example, a finite impulse response (FIR) filter.
Further, it is difficult to use equalizer circuits in clock recovery applications because prior art FIR filters form a portion of the clock recovery path. Thus, the signal delay introduced by prior art FIR filters interferes with accurate recovery of timing information present in the equalized signal output.
Accordingly, it would be advantageous to have an equalizer circuit and a method for equalizing data without quantizing the data prior to filtering the data.